int ledPin = 13;

void setup(){  
  Serial.begin(9600);
  Serial.setTimeout(200);
  pinMode(ledPin, OUTPUT);  
}  

void loop(){
  if (Serial.available()){
    String c = Serial.readString();
    if (c.equals("TONLED")) digitalWrite(ledPin, HIGH); 
    else if (c.equals("TOFFLED")) digitalWrite(ledPin, LOW);
    else Serial.print(c);
  }
}
